The "Masked Marvel" is one of Snoopy's popular alter egos. He was introduced in the strip from February 9, 1967. As the "Masked Marvel", Snoopy usually wears a black domino mask. On rare occasions, he also wears a cloak.
When he takes on the alter ego of the "Masked Marvel", Snoopy imagines himself as a world famous arm-wrestling champion. The alter ego's first appearance is part of a storyline in which Lucy is beating everybody in the neighborhood at arm-wrestling. She declares herself to be the world arm-wrestling champion.
Charlie Brown challenges Lucy to beat Snoopy as the "Masked Marvel". During a really tough and long arm-wrestling session, Snoopy kisses Lucy on the nose. Lucy declares that Snoopy made an unfair move by doing so. That makes Snoopy's victory invalid and means that Lucy is still the arm-wrestling champion.
This alter ego also appears in the TV special, It Was a Short Summer, Charlie Brown, in which the arm-wrestling storyline is adapted from the comic strip.
He makes a second appearance in the TV special, You're a Good Sport, Charlie Brown. In this special, the "Masked Marvel" signs up for the motocross race with Woodstock as his mechanic. The "Masked Marvel" in this special is similar to Snoopy's other alter ego from the comic strip, Joe Motocross.
The "Masked Marvel" makes a third appearance in the TV special, You're the Greatest, Charlie Brown. He represents the Ace Obedience School in the junior decathlon. He competes against Fremont Freddy, Marcie and Charlie Brown.